Optical crosstalk mitigation in lidar using digital signal processing

ABSTRACT

A method of detecting optical crosstalk in a LIDAR system includes selectively activating and deactivating light sources of a light source array; triggering a measurement of the field of view (FOV) during which at least one targeted region of the FOV is illuminated by the light source array and at least one non-targeted region of the FOV is not illuminated by the light source array; generating electrical signals based on at least one reflected light beam being received by a photodetector array, where the photodetector array comprises a targeted pixel group corresponding to the at least one targeted region of the FOV and a non-targeted pixel group corresponding to the at least one non-targeted region of the FOV; and detecting optical crosstalk that appears at at least one portion of the non-targeted pixel group based on electrical signals from the targeted pixel group and the non-targeted pixel group.

FIELD

The present disclosure relates generally to a device and to methods formitigating optical crosstalk in a Light Detection and Ranging (LIDAR)system.

BACKGROUND

Light Detection and Ranging (LIDAR), is a remote sensing method thatuses light in the form of a pulsed laser to measure ranges (variabledistances) to one or more objects in a field of view. In particular,light is transmitted towards the object. Single photodetectors or arraysof photodetectors receive reflections from objects illuminated by thelight, and the time it takes for the reflections to arrive at varioussensors in the photodetector array is determined. This is also referredto as measuring time-of-flight (TOF). LIDAR systems form depthmeasurements and make distance measurements by mapping the distance toobjects based on the time-of-flight computations. Thus, thetime-of-flight computations can create distance and depth maps, whichmay be used to generate images.

LIDAR systems that use a one-dimensional scanner have a weak point inoptical crosstalk. For example, in a situation where a highly reflectivetarget, such as a license plate, a traffic sign, or other type ofretro-reflector, is in the field of view, the LIDAR receiver detectstarget reflections across extended portions or even an entire portion ofthe Field of View (FOV) due to glare and scattering produced by theretro reflectors. This reflection produces a glare artefact that blocksthe LIDAR receiver from seeing essential parts of the scene resulting ina shadowing effect. Thus, objects located in the FOV covered by thisglare artefact or “shadow” may go undetected leading to inaccuracies inimaging and ultimately in safety issues in the field of autonomousdriving.

Therefore, an improved device that mitigates optical crosstalk due toartefacts caused by highly reflective objects may be desirable.

SUMMARY

According to one or more embodiments, a Light Detection and Ranging(LIDAR) system includes a LIDAR transmitter configured to scan a fieldof view with a plurality of light beams, each of the plurality of lightbeams having an oblong shape that extends perpendicular to a scanningdirection and a LIDAR receiver. The LIDAR transmitter includes a lightsource array comprising a plurality of light sources configured togenerate a scanning light bar such that each of the plurality of lightsources is configured to project into a different region of a pluralityof regions of the field of view; and a controller configured to triggera measurement of the field of view during which at least one targetedregion of the field of view is illuminated by the light source array andat least one non-targeted region of the field of view is not illuminatedby the light source array. The LIDAR receiver includes a photodetectorarray configured to receive at least one reflected light beam andgenerate electrical signals based on the at least one reflected lightbeam, wherein the photodetector array comprises a targeted pixel groupthat corresponds to the at least one targeted region of the field ofview and a non-targeted pixel group that correspond to the at least onenon-targeted region of the field of view; and an optical crosstalkdetection circuit configured to receive at least one first electricalsignal from the targeted pixel group and at least one second electricalsignal from the non-targeted pixel group, detect optical crosstalk thatappears at at least one portion of the non-targeted pixel group based onthe at least one first electrical signal and the at least one secondelectrical signal, and define a glare artefact box corresponding topixels of the photodetector array and defined by the detected opticalcrosstalk.

According to one or more embodiments, a method of detecting opticalcrosstalk in a LIDAR system is provided. The method includes oscillatinga one-dimensional microelectromechanical systems (MEMS) oscillatingstructure about a single axis such that light beams generated by aplurality of light sources of a linear light source array are projectedat different transmission directions into the field of view; selectivelyactivating and deactivating the plurality of light sources, wherein eachof the plurality of light sources is configured to project a light beamas a different segment of a scanning line into a corresponding region ofa plurality of regions of a field of view; triggering a measurement ofthe field of view during which at least one targeted region of the fieldof view is illuminated by the light source array and at least onenon-targeted region of the field of view is not illuminated by the lightsource array; generating electrical signals based on at least onereflected light beam being received by a photodetector array, whereinthe photodetector array comprises a targeted pixel group thatcorresponds to the at least one targeted region of the field of view anda non-targeted pixel group that correspond to the at least onenon-targeted region of the field of view; processing at least one firstelectrical signal from the targeted pixel group; processing at least onesecond electrical signal from the non-targeted pixel group; detectingoptical crosstalk that appears at at least one portion of thenon-targeted pixel group based on the at least one first electricalsignal and the at least one second electrical signal; and defining aglare artefact box corresponding to pixels of the photodetector arrayand defined by the detected optical crosstalk.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments are described herein making reference to the appendeddrawings.

FIG. 1 is a schematic diagram of a LIDAR scanning system in accordancewith one or more embodiments;

FIG. 2 is a schematic block diagram of a LIDAR scanning system inaccordance with one or more embodiments;

FIG. 3A shows an example of retro-reflector glare artefact according toone or more embodiments;

FIG. 3B shows an example of a point cloud of a 1D scanning LIDAR systemwith the retro-reflector glare artefact according to one or moreembodiments;

FIG. 4 shows an example of vertical crosstalk detected at aphotodetector array according to one or more embodiments;

FIG. 5 shows the example of a point cloud with the retro-reflector glareartefact shown in FIG. 3B, with an artefact box further definedaccording to one or more embodiments;

FIG. 6 shows a signal diagram of a photodetector array over ameasurement period t according to one or more embodiments; and

FIG. 7 is a schematic block diagram of a glare artefact processing chainaccording to one or more embodiments.

DETAILED DESCRIPTION

In the following, various embodiments will be described in detailreferring to the attached drawings. It should be noted that theseembodiments serve illustrative purposes only and are not to be construedas limiting. For example, while embodiments may be described ascomprising a plurality of features or elements, this is not to beconstrued as indicating that all these features or elements are neededfor implementing embodiments. Instead, in other embodiments, some of thefeatures or elements may be omitted, or may be replaced by alternativefeatures or elements. Additionally, further features or elements inaddition to the ones explicitly shown and described may be provided, forexample conventional components of sensor devices.

Features from different embodiments may be combined to form furtherembodiments, unless specifically noted otherwise. Variations ormodifications described with respect to one of the embodiments may alsobe applicable to other embodiments. In some instances, well-knownstructures and devices are shown in block diagram form rather than indetail in order to avoid obscuring the embodiments.

Connections or couplings between elements shown in the drawings ordescribed herein may be wire-based connections or wireless connectionsunless noted otherwise. Furthermore, such connections or couplings maybe direct connections or couplings without additional interveningelements or indirect connections or couplings with one or moreadditional intervening elements, as long as the general purpose of theconnection or coupling, for example to transmit a certain kind of signalor to transmit a certain kind of information, is essentially maintained.

Embodiments relate to optical sensors and optical sensor systems and toobtaining information about optical sensors and optical sensor systems.A sensor may refer to a component which converts a physical quantity tobe measured to an electric signal, for example a current signal or avoltage signal. The physical quantity may, for example, compriseelectromagnetic radiation, such as visible light, infrared (IR)radiation, or other type of illumination signal, a current, or avoltage, but is not limited thereto. For example, an image sensor may bea silicon chip inside a camera that converts photons of light comingfrom a lens into voltages. The larger the active area of the sensor, themore light that can be collected to create an image.

A sensor device as used herein may refer to a device which comprises asensor and further components, for example biasing circuitry, ananalog-to-digital converter or a filter. A sensor device may beintegrated on a single chip, although in other embodiments a pluralityof chips or also components external to a chip may be used forimplementing a sensor device.

In Light Detection and Ranging (LIDAR) systems, a light source transmitslight pulses into a field of view and the light reflects from one ormore objects by backscattering. In particular, LIDAR is a directTime-of-Flight (TOF) system in which the light pulses (e.g., laser beamsof infrared light) are emitted into the field of view, and a pixel arraydetects and measures the reflected beams. For example, an array ofphotodetectors receives reflections from objects illuminated by thelight.

Currently, a photodetector array may be used to measure the reflectedlight. The photodetector array may be a one-dimensional (1D) array thatconsists of multiple rows of photodetectors (pixels) arranged in asingle column or a two-dimensional (2D) array that consists of multiplerows and columns of photodetectors arranged in a grid-like arrangement.Each pixel row or group of adjacent pixel rows may be readout as ameasurement signal in the form of raw analog data. Each measurementsignal includes data from a single pixel.

Differences in return times for each light pulse across multiple pixelsof the pixel array can then be used to make digital 3D representationsof an environment or to generate other sensor data. For example, thelight source may emit a single light pulse, and a time-to-digitalconverter (TDC) electrically coupled to the pixel array may count fromthe time the light pulse is emitted, corresponding to a start signal,and record a time (i.e, a ToF hit time) the reflected light pulse isreceived at the receiver (i.e., at the pixel array), corresponding to aToF hit signal. The “time-of-flight” of the light pulse is thentranslated into a distance based on each recorded ToF hit time. MultipleToF hits are possible over a predefined measurement period. In thiscase, multiple TOF hit times are stored and the counter counts until theend of predefined measurement period, which is defined by a maximumdistance to be observed.

In another example, an analog-to-digital converter (ADC) may beelectrically coupled to the pixel array (e.g., indirectly coupled withintervening elements in-between) for pulse detection and ToFmeasurement. For example, an ADC may be used to estimate a time intervalbetween start/ToF hit signals with an appropriate algorithm.

For multiple hit, we do store multiple TOFs and counter counts until theend of measurement (defined by the maximum distance we want to observe).

A scan such as an oscillating horizontal scan (e.g., from left to rightand right to left of a field of view) can illuminate a scene in acontinuous scan fashion. Each firing of the laser beam by the lightsources can result in a scan line in the “field of view.” By emittingsuccessive light pulses in different scanning directions, an areareferred to as the field of view can be scanned and objects within thearea can be detected and imaged. Thus, the field of view represents ascanning plane having a center of projection. A raster scan could alsobe used.

FIG. 1 is a schematic diagram of a LIDAR scanning system 100 inaccordance with one or more embodiments. The LIDAR scanning system 100is an optical scanning device that includes a transmitter, including anillumination unit 10, a transmitter optics 11, and a one-dimensional(1D) MEMS mirror 12 (1D MEMS scanner), and a receiver, including aprimary optics 14, and an optical receiver 15. The optical receiver 15in the illustration is a 2D photodetector array 15 but may alternativelybe a 1D photodetector array. The receiver may further include receivercircuitry, such as data acquisition/readout circuitry and dataprocessing circuitry, as will be further described according to FIG. 2.

While horizontal scanning is depicted, the LIDAR scanning system 100 maybe rotated to scan in a different scanning direction. For example, theLIDAR scanning system 100 may be rotated 90° to scan in the verticaldirection instead of the horizontal direction.

The photodetector array 15, whether it be a 2D array or a 1D array, isarranged in such a manner that an intended field of view is mappedvertically on the vertical extension of the photodetector array 15. Areceived light beam will hit only a specific row or group or rows of thedetector array depending on the triggered light source and the verticalangle of the received light beam. The intended field of view may befurther mapped horizontally on the horizontal extension of a pixelcolumn, in the case of a 1D photodetector array, or mapped horizontallyon the horizontal extension of a 2D photodetector array. Thus, in asystem that uses a 1D photodetector array, each received light beam(i.e., each receiving line RL) is projected onto the column of thedetector array. In a system that uses a 2D photodetector array, eachreceived light beam (i.e., each receiving line RL) is projected onto oneof the columns of the detector array.

In this example, the illumination unit 10 is a laser array that includesthree light sources (e.g., laser diodes, light emitting diodes, or laserchannels) that are linearly aligned in single bar formation and areconfigured to transmit light used for scanning the field of view forobjects. The light emitted by the light sources is typically infraredlight although light with another wavelength might also be used. As canbe seen in the embodiment of FIG. 1, the shape of the light emitted bythe light sources is spread in a direction perpendicular to a scanningdirection to form a light beam with an oblong shape extending,lengthwise, perpendicular to the scanning direction. The illuminationlight transmitted from the light sources are directed towards thetransmitter optics 11 configured to focus each laser onto aone-dimensional MEMS mirror 12. The transmitter optics 11 may be, forexample, a lens or a prism.

When reflected by the MEMS mirror 12, the light from the light sourcesare aligned vertically to form, for each emitted laser shot, aone-dimensional vertical scanning line SL of infrared light or avertical bar of infrared light. Each light source of the illuminationunit 10 contributes to a different vertical region of the verticalscanning line SL. Thus, the light sources may be concurrently activatedand concurrently deactivated to obtain a light pulse with multiplevertical segments, where each vertical segment corresponds to arespective light source, However, each vertical region or segment of thevertical scanning line SL may also be independently active or inactiveby turning on or off a corresponding one of the light sources of theillumination unit 10. Thus, a partial or full vertical scanning line SLof light may be output from the system 100 into the field of view.

Accordingly, the transmitter of the system 100 is an optical arrangementconfigured to generate laser beams based on the laser pulses, the laserbeams having an oblong shape extending in a direction perpendicular to ascanning direction of the laser beams. As can be seen from FIG. 1, eachof the light sources is associated with a different vertical region inthe field of view such that each light source illuminates a verticalscanning line only into the vertical region associated with the lightsource. For example, the first light source illuminates into a firstvertical region and the second light sources illuminates into a secondvertical region which is different from the first vertical region.

Sequential scanning may be implemented by the transmitter via thecontroller in that one vertical region in the field of view isilluminated at a time. In particular, one light source may be activatedwhile all other light sources are deactivated. Thus, the plurality oflight sources are sequentially activated in this manner to sequentiallytransmit at different vertical regions in the field of view.

In addition, while three laser sources are shown, it will be appreciatedthat the number of laser sources is configurable and is not limitedthereto. For instance, the vertical scanning line SL may be generated bytwo or more laser sources.

In one example, 32 pixels may be arranged in a single pixel column andeight light sources may be used. In this case, each light sourcecorresponds to one of eight different vertical regions of the field ofview. Thus, each light source may also be mapped to a different group offour pixels (i.e., four pixel rows), wherein each group is mutuallyexclusive. In essence, each group of pixel is mapped to one of eightdifferent vertical regions of the field of view. Different groups ofpixels can be fired at by activating its corresponding light source,whereas other groups may not be fired at by deactivating itscorresponding light source.

Pixels that are intended to be fired at (e.g., due to activating acorresponding light source) may be referred to as targeted pixels. Incontrast, pixels that are not intended to be fired at (e.g., due todeactivating a corresponding light source) may be referred to as non-targeted pixels. It is noted that even though non-targeted pixels arenot intended to be fired at, and thereby not intended to receivereflected laser light, non-targeted pixels may still receive and detectlight from both glare artefacts (i.e., reflected laser light artefacts)that are reflected by retro-reflectors and ambient light (i.e., noise).

In the sequential scanning scheme in which vertical regions of the fieldof view are sequentially targeted, one group of pixels are designated asa targeted group including targeted pixels such that the groups ofpixels are sequentially targeted while the remaining pixel groups ineach scan are designated as non-targeted groups made up of non-targetedpixels.

The MEMS mirror 12 is a mechanical moving mirror (i.e., a MEMSmicro-mirror) integrated on a semiconductor chip (not shown). The MEMSmirror 12 according to this embodiment is configured to rotate about asingle scanning axis and can be said to have only one degree of freedomfor scanning. Distinguished from 2D-MEMS mirrors (2D MEMS scanners), inthe 1D MEMS mirror, the single scanning axis is fixed to a non-rotatingsubstrate and therefore maintains its spatial orientation during theoscillation of the MEMS mirror. Due to this single scanning axis ofrotation, the MEMS mirror 12 is referred to as a 1D MEMS mirror or 1DMEMS scanner. However, it will be appreciated that a 2D MEMS mirror maybe used in the LIDAR scanning system 100 instead of a 1D MEMS mirror aslong as non-targeted pixel groups are used for detecting opticalcrosstalk, to be described below.

The MEMS mirror 12 is configured to oscillate “side-to-side” about asingle scanning axis 13 such that the light reflected from the MEMSmirror 12 (i.e., the vertical scanning line of light) oscillates backand forth in a horizontal scanning direction. A scanning period or anoscillation period is defined, for example, by one complete oscillationfrom a first edge of the field of view (e.g., left side) to a secondedge of the field of view (e.g., right side) and then back again to thefirst edge. A mirror period of the MEMS mirror 12 corresponds to ascanning period.

Thus, the field of view is scanned in the horizontal direction by thevertical bar of light by changing the angle of the MEMS mirror 12 on itsscanning axis 13. For example, the MEMS mirror 12 may be configured tooscillate between +/−15 degrees in a horizontal scanning direction tosteer the light over +/−30 degrees (i.e., 60 degrees) making up thehorizontal scanning range of the field of view. In this case,transmission optics (not illustrated) are used to extend the field ofview by increasing (e.g., doubling) the angular range of transmittedlight from the MEMS mirror 12. Thus, the field of view may be scanned,line-by-line, by a rotation of the MEMS mirror 12 though its degree ofmotion. One such sequence though the degree of motion (e.g., from −15degrees to +15 degrees or vice versa) is referred to as a single scan.Thus, two scans are used for each scanning period. Different regions(e.g., different vertical regions) of the field of view may be targetedduring each scan or scanning period. Multiple scans may be used togenerate distance and depth maps, as well as 3D images by a processingunit.

While the transmission mirror is described in the context of a MEMSmirror, it will be appreciated that other mirrors can also be used. Inaddition, the degree of rotation is not limited to +/−15 degrees, andthe field of view may be increased or decreased according to theapplication. Thus, a one-dimensional scanning mirror is configured tooscillate about a single scanning axis and direct the laser beams atdifferent directions into a field of view. Hence, a transmissiontechnique includes transmitting the beams of light into the field ofview from a transmission mirror that oscillates about a single scanningaxis such that the beams of light are projected as a vertical scanningline SL into the field of view that moves horizontally across the fieldof view as the transmission mirror oscillates about the single scanningaxis.

LIDAR systems using 1D-scanning mirrors can use a more relaxed shot-rateof the illumination unit 10 (i.e., transmitter) compared to 2D-scanningmirrors which use laser points for scanning the field of view whichrequires more shots for the transmitter to scan a field of view. Inaddition, LIDAR systems using 1D-scanning mirrors are typically morerobust against shock and vibrations when compared to 2D-scanning mirrorsand are therefore well suited for automotive applications.

Upon impinging one or more objects, the transmitted bar of verticallight is reflected by backscattering back towards the LIDAR scanningsystem 100 as a reflected vertical line where the second opticalcomponent 14 (e.g., a lens or prism) receives the reflected light. Thesecond optical component 14 directs the reflected light onto thephotodetector array 15 that receives the reflected light as a receivingline RL and is configured to generate electrical measurement signals.For example, second optical component 14 projects the received reflectedlight onto targeted pixels of the pixel array 15. However, as will bediscussed, non-targeted pixels may also receive reflected light due tooptical crosstalk (e.g., due to a reflection by a retro-reflector). Theelectrical measurement signals may be used for generating a 3D map ofthe environment and/or other object data based on the reflected light(e.g., via TOF calculations and processing).

The receiving line RL is shown as a vertical column of light thatextends along the pixel column in a lengthwise direction of the pixelcolumn. The receiving line has three vertical regions that correspond tothe vertical regions of the vertical scanning line SL shown in FIG. 1.As the vertical scanning line SL moves horizontally across the field ofview, each light beam (i.e., each receiving line RL) is projected ontothe column of the detector array 15. The transmission direction of thescanning ling SL set by the rotation angle of the MEMS mirror 12 ismapped to an image column of an image structure mapped to the field ofview.

The photodetector array 15 can be any of a number of photodetectortypes; including avalanche photodiodes (APD), photocells, and/or otherphotodiode devices. Imaging sensors such as charge-coupled devices(CCDs) can be the photodetectors. In the examples provided herein, thephotodetector array 15 is a one-dimensional (1D) APD array thatcomprises an array of APD pixels arranged in a single column. Asprovided herein, “photodiodes” and “pixels” are used interchangeably.

Moreover, the photodetector array 15 is a static the photodetector array15. Meaning, all pixels are activated and are capable of being readoutat all times via a corresponding readout channel. As a result, eachpixel is fixedly assigned and coupled to a readout channel so that anytime a pixel generates an electrical signal, the signal can be read out.pixels Thus, receiver circuitry may receive electrical signals via thereadout channels from both targeted and non-targeted pixels. All pixelscan be read out for each discrete transmission angle of the MEMS mirror12.

A measurement period may be defined for each discrete transmission angleduring which a receiver circuit monitors for electrical signalsgenerated by the photodetector array 15. For example, the measurementperiod may start at a transmission time of the laser and may lapse aftera predetermined time period thereafter (e.g., after 2 μs). A pixel mayreceive multiple reflections during the measurement period correspondingto backscattering occurring at objects located at different distances.In other words, a pixel may receive multiple reflected light pulses atdifferent times over the measurement period, where each pulsecorresponds to a different object distance.

The photodetector array 15 receives reflective light pulses as thereceiving line RL and generates electrical signals in response thereto.Since the time of transmission of each light pulse from the illuminationunit 10 is known, and because the light travels at a known speed, atime-of-flight computation using the electrical signals can determinethe distance of objects from the photodetector array 15. A depth map canplot the distance information.

In one example, for each distance sampling, a controller triggers alaser pulse from each of the light sources of the illumination unit 10and also starts a timer in a Time-to-Digital Converter (TDC) IntegratedCircuit (IC). This can also be performed using a field-programmable gatearray (FPGA). The laser pulse is propagated through the transmissionoptics, reflected by the target field, and captured by one or morereceiving photodiodes of the photodetector array 15. Each receivingphotodiode emits a short electrical pulse that is read out by the analogreadout circuit. Each signal that is read out of the analog readoutcircuit may be amplified by an electrical signal amplifier.

A comparator IC recognizes the pulse and sends a digital signal to theTDC to capture the timer value corresponding to the ToF hit time tocapture the time-of-flight. The TDC uses a clock frequency to calibrateeach measurement. The TDC sends the serial data of the differential timebetween the start and ToF hit digital signals to the controller, whichfilters out any error reads, averages multiple time measurements, andcalculates the distance to the target at that particular field position.By emitting successive light pulses in different directions establishedby the MEMS mirror 12, an area (i.e., a field of view) can be scanned, athree-dimensional image can be generated, and objects within the areacan be detected.

The signal processing chain of the receiver may also include an ADC foreach photodiode. The ADC is configured to convert the analog electricalsignals from the photodiode into a digital signal that is used forfurther data processing.

In addition, instead of using the TDC approach, ADCs may be used forsignal detection and ToF measurement. For example, each ADC may be useddetect an analog electrical signal from one or more photodiodes toestimate a time interval between a start signal (i.e., corresponding toa timing of a transmitted light pulse) and a ToF hit signal (i.e.,corresponding to a timing of receiving an analog electrical signal at anADC) with an appropriate algorithm.

When a pulse of laser energy as a vertical scanning line SL enters thefield of view from the surface of MEMS mirror 12, reflective pulsesappear when the laser light illuminates an object in the field of view.These reflective pulses arrive at the photodetector array 15 as a bar oflight that may span vertically across one or more pixels. That is, allphotodetector pixels in a pixel column (e.g., if all light sources aretriggered) or a portion of the photodetector pixels (e.g., if only aportion of the light sources are triggered) may receive reflected laserlight. For example, in one instance, all light sources of theillumination unit 10 may be used to generate the scanning lineSL/receiving line RL. In this case, the receiving line RL may extendalong the full pixel column in the lengthwise direction. In anotherinstance, only a subset of the light sources may be used to generate thescanning line SL/receiving line RL. In this case, the receiving line mayextend along only a portion of the pixel column in the lengthwisedirection.

The photodetector array 15 is configured to generate measurement signals(electrical signals) used for generating a 3D map of the environmentbased on the received reflected light and the transmissionangle/direction of a corresponding transmitted beam (e.g., via TOFcalculations and processing). While not shown, the LIDAR scanning system100 may also include a digital micromirror device (DMD) and a secondaryoptics (e.g., a lens, a total internal reflection (TIR) prism, or a beamsplitter) that are configured to initially receive the reflected lightthrough the primary optics 14, and redirect the received reflected lighttowards the photodetector array 15. For example, the DMD would firstreceive the reflected light pulse from the primary optics, and deflectthe received reflected light through the secondary optics (e.g., a lens,a total internal reflection (TIR) prism, or a beam splitter) onto thephotodetector array 15. In this case, the photodetector array 15 wouldstill receive a vertical column of light, as described above.

FIG. 2 is a schematic block diagram of the LIDAR scanning system 200 inaccordance with one or more embodiments. In particular, FIG. 2 showsadditional features of the LIDAR scanning system 200, including exampleprocessing and control system components such as a MEMS driver, areceiver circuit, and a system controller.

The LIDAR scanning system 200 includes a transmitter unit 21 that isresponsible for an emitter path of the system 200, and a receiver unit22 that is responsible for a receiver path of the system 200. The systemalso includes a system controller 23 that is configured to controlcomponents of the transmitter unit 21 and the receiver unit 22, and toreceive raw data from the receiver unit 22 and perform processingthereon (e.g., via digital signal processing) for generating object data(e.g., point cloud data). Thus, the system controller 23 includes atleast one processor and/or processor circuitry (e.g., comparators anddigital signal processors (DSPs), a dedicated IC, or a FPGA) of a signalprocessing chain for processing data, as well as control circuitry, suchas a controller, that is configured to generate control signals. Thecontroller may be a FPGA that generates the control signals. The LIDARscanning system 200 may also include a sensor 26, such as a temperaturesensor, that provides sensor information to the system controller 23.

The transmitter unit 21 includes the illumination unit 10, the MEMSmirror 12, and a MEMS driver 25 configured to drive the MEMS mirror 12.In particular, the MEMS driver 25 actuates and senses the rotationposition of the mirror, and provides position information (e.g., tiltangle or degree of rotation about the rotation axis) of the mirror tothe system controller 23. Based on this position information, the lasersources of the illumination unit 10 are triggered by the systemcontroller 23 and the photodiodes are activated to sense, and thusmeasure, a reflected light signal. Thus, a higher accuracy in positionsensing of the MEMS mirror results in a more accurate and precisecontrol of other components of the LIDAR system.

The receiver unit 22 includes the photodetector array 15 as well as areceiver circuit 24 that includes an analog readout circuit, includingtransimpedance amplifiers (TIAs), and a digital readout circuit,including analog-to-digital converters (ADCs).

The analog readout circuit includes N analog output channels (e.g., 32channels) each configured to read out measurement signals received froman assigned pixel of the photodetector array 15. One acquisition ofanalog data from the photodetector array 15 on an analog output channelmay be referred to as an analog sample, and each analog output channelmay be used to acquire different analog samples. Each sample furthercorresponds to a sample time, at which time measurement signals are readout from the corresponding pixel.

Thus, the receiver circuit 24 may receive the analog electrical signalsfrom the photodetectors of the photodetector array 15 and transmit theelectrical signals as raw analog data to a single bit or a multibit ADC.A single bit ADC outputs a one bit signal each time a TOF hit isdetected. The one bit signal simply indicates that a reflected signalpulse was received. In contrast, a multibit ADC outputs a multibitsignal that additionally includes amplitude information corresponding tothe intensity of the reflected signal pulse.

Prior to the ADC receiving the electrical signals, the electricalsignals from each channel may pass through a corresponding amplifier(e.g., a transimpedance amplifier (TIA)) of N amplifiers that convertsthe electrical signals from, for example, current into voltage. In thecase of one bit signal processing, a TIA may be used without an externalADC coupled thereto. TIAs have a comparator at their output, which is aone-bit ADC. Thus, an additional ADC external to the TIA is not neededin this circumstance and only a TIA may be used.

Thus, each TIA and each ADC are incorporated in the receiver circuit 24.One acquisition of ADC data may be referred to as an ADC sample, whichmay also be referred to as a digital sample. Each sample furthercorresponds to a sample time, at which time measurement signals are readout from one or more pixels.

The ADCs are configured to convert the raw analog data into raw digitaldata for transmission to the system controller 23, which performsfurther processing on the raw digital data, including averaging andpulse detection, crosstalk analysis and mitigation, and generating 3Dpoint cloud data. Thus, each of the analog output channels is coupled toa corresponding ADC of N ADCs that is configured to convert the analogdata from a respective analog output channel into digital data. As aresult, the receiver circuit 24 also includes a digital readout circuitof N digital output channels, each being coupled to a differentcorresponding analog output channel via a different corresponding ADC.

The receiver circuit 24 may also receive trigger control signals fromthe system controller 23 that triggers an activation of all thephotodetectors for a measurement period. The receiver circuit 24 mayalso receive gain setting control signals for controlling the gain ofone or more photodetectors.

The system controller 23 includes signal processing circuitry thatreceives the raw digital data as well as serial data of a differentialtime between start and ToF hit digital signals generated by an ADC, anduses the received data to calculate time-of-flight information for eachfield position within the field of view, to generate object data (e.g.,point cloud data), and to generate a 3D point cloud.

Acquired LIDAR data includes data from a reflected object signal,originating from a LIDAR transmitted laser beam reflecting off anobject, and a noise signal, originating from other light sources such asambient light (e.g., from the sun). Ambient noise typically has asmaller magnitude when compared to a reflected object laser signal.

FIG. 3A shows an example of retro-reflector glare artefact 300 accordingto one or more embodiments. In this case, the reflector is located inthe middle of the cross-like reflection, also referred to as a crosstalkartefact. The artefact 300 is made up by vertical crosstalk that extendsalong a vertical axis and horizontal crosstalk that extends along ahorizontal axis.

FIG. 3B shows an example of a point cloud of a 1D scanning LIDAR systemwith the retro-reflector glare artefact 300 according to one or moreembodiments. In this case, the retro-reflector glare artefact 300 blocksthe receiver from seeing parts of the scene corresponding to sametime-of-flight as the reflector. In other words, objects locates at thesame distance as the reflector are obscured by the retro-reflector glareartefact 300 and may go undetected. This produces a shadow 400 in thepoint cloud.

FIG. 4 shows an example of vertical crosstalk detected at photodetectorarray 15 according to one or more embodiments. FIG. 4 includes a signaldiagram of a photodetector array over a measurement period t. Atime-of-flight (TOF) is charted over a measurement period t. Thetime-of-flight starts at zero to coincide with the firing of the laserbeam and ends at the end of the measurement period t. The measurementperiod t is a predetermined (i.e., limited) amount of time during whichelectrical pulses are read out for a single sample period. Anyelectrical pulses generated by the photodetector array 15 are read outand processed. The measurement period t is an amount of time duringwhich reflected light can be expected to be received. After theexpiration of the measurement period, a new sampling of the FOV can beperformed, including a new laser beam transmission with the measurementperiod being reset and new set of TOF measurements being taken.

Turning back to FIG. 4, the time-of-flight progresses from zero towardsmeasurement period t based on the time it takes for a return pulse to bedetected. Pixels that detect a light pulse at the same time generate acorresponding electrical pulse that coincides with the sametime-of-flight time, referred to as a time-of-fight index. In theory, itwould be said that these pixels that generate an electrical pulse at thesame time-of-fight index detect one or more objects having a samedistance from the photodetector array 15.

However, in this case, a light source of illumination unit 10 fires alaser beam that is reflected by a retro-reflector 40 and is incident ona single pixel APD(n) of the photodetector array 15. This pixel APD(n)may be referred to as a retro-reflector pixel, as it correspond to theactual location of the retro-reflector. There may be two or moreretro-reflector pixels depending on the size or distance of theretro-reflector object. Those pixels adjacent to the retro-reflectorpixel that experience crosstalk may be referred to as crosstalk pixelsor simply neighboring pixels.

The return echo from retro-reflector 40 on pixel APD(n) is so strongthat it appears on neighboring channels in the electrical domain. Thus,the highly reflective object causes leakage in the electrical domaininto neighboring pixels APD(n−1), APD(n−2), APD(n+1), and APD(n+2). Thiseffect may also be seen from low reflective objects located at a closerange to the photodetector array 15. This may lead to a false reading bythe neighboring pixels that an object is present at the sametime-of-flight distance that corresponds to the electrical pulsegenerated by pixel APD(n).

In order to mitigate crosstalk between pixels, certain system propertiesmay be used in one or more combinations.

First, a 1D scanning system may be implemented that uses a scanninglaser bar and a static receiver pixel array.

Second, the laser may follow a sequential firing pattern such that onlya portion of the vertical regions of the field of view is illuminated ata given time. This can be done by only triggering a portion of the lightsources at a time, leaving other light sources deactivated. Thus, foreach laser beam transmission there exists a group of targeted pixels andnon-targeted pixels.

Third, the photodetector array can be read out at all times, even forthe untargeted part of the field of view.

Fourth, the receiver circuit 24/system controller 23 is configured todetect multiple target reflections per pixel/angle measurement. In otherwords, the photodetector array 15 is capable of generating multipleelectrical pulses at different time-of-flights in a measurement period,even by the same pixel, and the receiver circuit 24/system controller 23is configured to receive these multiple electrical pulses over themeasurement period.

When the laser illuminates only a part of the field of view, normallythe untargeted pixels of the photodetector array 15 will not produce anyoutput signal other than noise produced by ambient-light induced noise.Such electrical pulses are small and can be filtered out bythresholding. However, when the laser beam or laser sidelobes hit aretro-reflector, the pixels across that horizontal or vertical part ofthe field of view will actually trigger and return a signal that may beinterpreted as if an actual target is producing a reflection for thatspecific pixel, angle, and distance. Said differently, the signalproduced by vertical or horizontal crosstalk may be interpreted as a hiton an object in the field of view for that specific pixel, angle, anddistance when no such object at that specific pixel, angle, and distanceexists.

Crosstalk artifacts share common properties that can be used to detectthe artefacts in one or more combinations.

Vertical crosstalk artefacts share a common angle. Thus, an apparentobject detected at a same transmission angle over multiple adjacentpixels may be one indicator for vertical crosstalk.

Both vertical and horizontal crosstalk share a common distance (i.e.,time-of-flight). That is because reflected light related to glareartefacts arrive at the neighboring pixels of the photodetector array 15at the same time (i.e., at the same time-of-flight) the “real” reflectedlight is received from the actual location of the retro-reflector.

Furthermore, for vertical crosstalk, pulse amplitudes generated by theneighboring pixels are inversely related to distance from theretro-reflector pixel. Thus, neighboring pixels further away from theretro-reflector pixel should generate electrical pulses that have asmaller amplitude than neighboring pixels that are close to theretro-reflector pixel. A decrease in amplitude across multipleneighboring pixels with increasing distance from the retro-reflectorpixel may be an indicator of vertical crosstalk.

Additionally, for horizontal crosstalk, pulse amplitudes generated bythe neighboring pixels are inversely related to position of theretro-reflector with respect to transmission angle. For example, ifconsidering a retro-reflector is located at a first transmission angleand is detected by the retro-reflector pixel, the retro-reflector pixelmay detect a weaker reflected signal at a second transmission angleadjacent to the first transmission angle. Moreover, the retro-reflectorpixel may detect an even weaker reflected signal at a third transmissionangle adjacent to the second transmission angle, where the secondtransmission angle is between the first and the third transmissionangles. This may occur in both horizontal directions from the firsttransmission angle. This decrease in pulse amplitude in the horizontaldirections by the same pixel may be an indicator of horizontalcrosstalk.

In a 2D photodetector array, neighboring pixels in the horizontaldirection can be evaluated for horizontal crosstalk in a similar mannerdescribed for vertical crosstalk. A targeted pixel or group of pixelsmay correspond to both an activated light source and a transmissionangle and a non-targeted pixel or group of pixels may correspond to thesame light source but one or more different transmission angles. In theevent a targeted pixel is a retro-reflector pixel, those neighboring,non-target pixels horizontal to the targeted pixel may be evaluatedwhere pulse amplitudes at the neighboring, non-targeted pixels areinversely related to the position of the targeted pixel.

By combining two or more crosstalk indicators and recording thetransmission angle, pixel number, and distance, a probability ofidentifying a crosstalk pixel is increased and steps can be taken by aDSP to mitigate the identified crosstalk event and possibly remove glareartefacts from the point cloud.

A three step approach may be used for crosstalk analysis and mitigation:detection and flagging, artefact probability scoring, and probabilitythresholding.

The first step is referred to as detection and flagging. This processincludes sequential scanning, reading out and monitoring untargetedpixels, and flagging TOF hits based on common artefact propertiesderived from the untargeted pixels.

Sequential firing includes reading the full photodetector array 15,including both targeted and untargeted pixels for every laser shot overa measurement period. Typically, a single shot signal-to-noise ratio(SNR) is already sufficient for reliable flagging. If untargeted pixelsproduce an output signal (i.e., an electrical pulse), the systemcontroller 23 is configured to record the transmission anglecorresponding to the rotation angle of the MEMS mirror 12, the pixelnumber of the untargeted pixel that generates the signal, and the TOF(i.e., the distance).

The system controller 23 also flags the area containing the artefacts inthe point cloud corresponding to the TOF and transmission angle todefine an artifact box.

This step includes identifying potential artefact areas in the LIDARpoint-cloud by observing unilluminated (i.e., untargeted) parts of theLIDAR FOV. The untargeted parts of the FOV are those regions in the FOVcorresponding to deactivated light sources, and further correspond tountargeted pixels of the photodetector array 15. As noted above,normally the untargeted pixels of the photodetector array 15 will notproduce any output signal other than noise produced by ambient-lightinduced noise. Thus, the presence of an electrical pulse at anuntargeted pixels, for example, greater than a noise signal level, maybe indicative of an abnormality such as pixel crosstalk.

By monitoring the untargeted pixels of the photodetector array 15, whereelectrical signals are expected to be below a threshold value, thesystem controller 23 can detect the potential presence of aretro-reflector, defined by firing angle, pixel number, and distance.With this information, the receiver processing defines a “bounding box”or an “artefact box” in the field of view. FIG. 5 shows the example ofthe point cloud with the retro-reflector glare artefact 300 shown inFIG. 3B, with an artefact box 500 further defined by the systemcontroller 23. As can be see, areas in the point cloud that correspondto untargeted pixels are used to define the artefact box. The targetreflections received within the artefact box are flagged by the systemcontroller 23 for further analysis.

The second step is referred to as artefact probability scoring. Thisstep includes analyzing the potential artefact areas by checking if theartefact is “transparent” and assigning each TOF hit a probabilityscore. Here, the system controller 23 applies a probability scoringalgorithm in which every detected hit starts with a probability score of100%. The probability scoring algorithm checks the flagged targetreflections from step 1 for additional reflections at a differenttime-of-flight.

For example, FIG. 6 shows a signal diagram of a photodetector array overa measurement period t according to one or more embodiments. In thiscase, each pixel of the photodetector array generates an electricalpulse at a first time-of-flight TOF1, which may be indicative ofvertical crosstalk. Additionally, pixel APD(n−2) generates a secondelectrical pulse at a second time-of-flight TOF2, where TOF1 correspondsto a first object distance and TOF2 corresponds to a second, furtherobject distance at a same transmission angle. Here, it can be said thatthe electrical pulse at TOF2 is behind the artefact box because itoccurs later in time.

If the same pixel (e.g., APD(n−2)) and the same transmission anglecontains one or more reflections behind the artefact box, this indicatesthat the perceived target detected within the artefact box was actuallytransparent, allowing laser light to pass therethrough and be reflectedby a more distant object. This indicates a high likelihood that thereflection detected by the pixel at TOF1 was actually a retro-reflectorglare artefact. In this case, the probability score is lowered with apredefined fraction for every additional detected target in the samepixel/angle combination.

For instance, a probability modifying fraction may be set to 75%. When aperceived target within the artefact box has three additional targetsbehind it (i.e., three additional electrical pulses), the resultingprobability score would be 0.75*0.75 *0.75=42%.

Thus, if pixels contain further TOF hits after a flagged distancecorresponding to the distance of the artefact box, the system controller23 decreases the likelihood score for the affected pixel/hit, whichcoincidently increase the likelihood that the hit at the flaggeddistance is an artefact. Flagged pixels without more hits likely definesthe actual location of the retro-reflector. Additionally, actual targetswill not have been flagged.

In summary for step 2, the system controller 23 generates an artefactlikelihood score per TOF hit for each pixel, checks whether a pixelcontains more than one hit, checks a distance and amplitude correlation(if amplitude is available), and determines that pixels without morehits are valid targets, while decreases the probability that a TOF hitis valid if it is followed by one or more additional TOF hits in thesame measurement period.

The third step is referred to as probability thresholding. This stepincludes mitigating the potential artefact areas through thresholdingand artefact reporting. Upon completing step 2, the system controller 23has recorded a probability score for each TOF hit for each pixel. Thesystem controller 23 may compare each probability score to a predefinedprobability threshold, and discard any TOF hits with a probability scoreless than the predefined probability threshold. For example, apredefined probability threshold of 50% would result in any TOF hithaving a probability score less than 50% be discarded and not reported(output) to the system controller 23.

Alternatively, the system controller 23 may transmit the probabilityscore for each TOF hit as part of the point cloud output protocol (i.e.,along with the digital measurement data), such that the vehicle'sartificial intelligence can decide what to do with low probabilitytargets.

The system controller 23 may also perform likelihood thresholding duringwhich a laser beam is transmitted in the same vertical region of the FOVat the same transmission angle multiple times, and the number of TOF hisis counted to generate a likelihood histogram. For example, if a laserbeam is shot in the above manner eight times, eight TOF hits mayindicate a certain target, some number of intermediary number of hits(e.g., two to six hits) may indicate potential glare or crosstalk, and alow number of hits (e.g., less than two) may indicate an interferer orfalse hit. The system controller 23 may than only report TOF hits abovea likelihood threshold to a point cloud processor, or report thelikelihood score to the to a point cloud processor or other vehicleartificial intelligence along with the digital measurement data.

FIG. 7 is a schematic block diagram of a glare artefact processing chain700 according to one or more embodiments. In particular, the glareartefact processing chain 700 is incorporated in the receiver unit 22and the system controller 23 of the LIDAR system 200, where the receivercircuit 24 includes TIAs and ADCs, and the system controller 23 receivesthe digital raw data from the ADCs and includes further digital signalprocessing, crosstalk detection and analysis, and point cloudgeneration.

In this example, the photodetector array 15 is 2×32 APD array having twopixel columns, 32 pixel rows, and 64 pixels in total. The glare artefactprocessing chain 700 includes a plurality of TIAs 31-34 coupled toassigned pixels of the photodetector array 15. In particular, each TIAis coupled to a fixed group of adjacent pixels in both pixel columns via16 analog readout channels. As a result, TIA 31 is coupled to the pixelsin columns 1 and 2, rows 1-8 TIA 32 is coupled to the pixels in columns1 and 2, rows 9-16; TIA 33 is coupled to the pixels in columns 1 and 2,rows 17-24; and TIA 34 is coupled to the pixels in columns 1 and 2, rows25-32.

As such, each TIA receives 8 line from a first APD column and another 8lines from a second APD column for defined channels (i.e, each TIA isprocessing 8 channels for each APD column). The output of each TIAincludes 8 LVDS lines or 8 analog outputs if external ADCs are used. Inthe latter case, the input to the DSP line is some interface providingn-bit digital data for 8 APD channels).

Alternatively, TIA 31 may be coupled to the pixels in column 1, rows1-16; TIA 32 may be coupled to the pixels in column 1, rows 17-32; TIA33 may be coupled to the pixels in column 2, rows 1-16; and TIA 34 maybe coupled to the pixels in column 2, rows 17-31, or some otherconfiguration.

The pixel rows may be arranged into sub-groups that are each mapped to adifferent vertical region in the field of view. Each sub-group of rowsfurther corresponds to and is mapped to a different light source of theillumination unit 10. For example, a first sub-group may include pixelrows 1-8 that are mapped to a first (i.e., an uppermost) vertical regionin the field of view and mapped to a first light source or a first pairof light sources. A second sub-group may include pixel rows 9-16 thatare mapped to a second (i.e., a second uppermost) vertical region in thefield of view and mapped to a second light source or a second pair oflight sources. A third sub-group may include pixel rows 17-24 that aremapped to a third (i.e., a second lowermost) vertical region in thefield of view and mapped to a third light source or a third pair oflight sources. A fourth sub-group may include pixel rows 25-32 that aremapped to a fourth (i.e., a lowermost) vertical region in the field ofview and mapped to a fourth light source or a fourth pair of lightsources.

As a result of the mapping to different pixel sub-groups, the systemcontroller 23 is configured to track which pixels and channels aretargeted pixels/targeted channels that correspond to a triggered lightsource. Similarly, the system controller 23 is configured to track whichpixels and channels are non-targeted pixels/non-targeted channels thatcorrespond to non-triggered light sources.

In addition, when implementing a 2D photodetector array, the systemcontroller 23 also tracks which pixel column is targeted and which pixelcolumn(s) is not targeted based on the transmission angle of the MEMSmirror 12.

The receiver chain reads out and processes all pixels simultaneously.Each TIA 31-34 converts the electrical signals generated by its assignedpixels from, for example, a current into a voltage. Each TIA 31-34 hastwo sets of output channels, each set corresponding to a differentsub-group of pixel rows (i.e., sub-group of pixels). As a result, oneset of output channels from a TIA may output voltage signalscorresponding to eight targeted pixels and the other set of outputchannels from the TIA may output voltage signals corresponding to eightnon-targeted pixels depending on which vertical region of the field ofview is targeted by a laser beam. Alternatively, both sets of outputchannels from a TIA may output voltage signals corresponding to eightnon-targeted pixels depending on which vertical region of the field ofview is targeted by a laser beam. Each TIA output is differentialmeaning the number of lines is the number of channels times two. Inparticular, low-voltage differential signaling (LVDS) signals from theTIA are used as an input to a FPGA. Single line would have the sameeffect, but LVDS signals has some advantages on signal integrity and lowpower when it comes to switching (e.g., lower the gap between thechannels).The output channels from the TIAs 31-34 are coupled tooptional ADCs 41-48. The ADCs 41-48 are configured to convert the analogvoltage signals into digital ADC samples, each of which correspond to aTOF index (i.e., a TOF hit time or distance). In the case of one bitsignal processing, a TIA may be used without an external ADC coupledthereto. TIAs have a comparator at their output, which is a one-bit ADC.Thus, an additional ADC external to the TIA is not needed in thiscircumstance and only a TIA may be used. A one-bit ADC integrated in aTIA may merely indicate a detection of a TOF hit, whereas a multibitADC, external to a TIA, may additionally provide amplitude informationfor each TOF hit. In the event that there are multiple TOF hits on apixel in a measurement period, a TIA or an ADC may output multiple ADCsamples at different times over the measurement period for thatrespective pixel.

The output channels of the ADCs 41-48 are coupled to a DSP lineprocessing circuit 50 that is configured to receive the ADC samples fromthe ADCs 41-48 and perform averaging and pulse detection. As part of thepulse detection, the DSP line processing circuit 50 may be configured toperform TOF measurements (i.e., distance measurements), pulse magnitude(i.e., amplitude) measurements, and pulse length measurements for eachpixel and record the corresponding values for each pixel according topixel number.

In addition, a histogram may be used to sum and average the detectedpulses over a plurality of measurements. For example, a laser may befired at the same vertical region at the same angle eight times toobtain eight samples, and the DSP line processing circuit 50 maycalculation the average of the number of samples for each respectivepixel.

The presence or absence of the histogram is open to design choice.Having it present increases the required resources, but improves thereliability of the artefact box. Omitting it would be an implementationoptimization at the cost of losing artefact detection at longerdistances.

The DSP line processing circuit 50 also includes a multiplexerconfigured to receive targeted pixel information and selectively outputdetected pulse information to either the targeted scene processingcircuit 61 or to the non-targeted scene processing circuit 62 based onthe received targeted pixel information.

The targeted pixel information indicates which pixels of the pixel arrayare targeted pixels based on the targeted vertical region of the fieldof view (i.e., based on the triggered light source(s)) and possibly thetransmission angle. By the process of elimination, the targeted pixelinformation also indicates which pixels of the pixel array arenon-targeted pixels. Thus, the multiplexer is configured to selectivelyoutput pulse information to the respective processing block 61 or 62.For the example given, there are 8 targeted APD channels that result in8 lines being output from the DSP line processing circuit 50 to thetargeted scene processing circuit 61. The remaining 24 APD channelscorrespond to non-targeted APD pixel lines, meaning that there are 24lines being output from the DSP line processing circuit 50 to thenon-targeted scene processing circuit 62. The number of targeted APDchannels is configurable. For example, 4 APD channels may be targetedinstead of 8, resulting in 28 non-targeted APD channels.

The targeted scene processing circuit 61 is configured to receive pulseinformation corresponding to electrical signals generated by targetedpixels, determine detected TOF hits, and output the detected TOF hits tothe crosstalk processing circuit 70.

The non-targeted scene processing circuit 62 is configured to receivepulse information corresponding to electrical signals generated bynon-targeted pixels, determine detected TOF hits, define a bounding boxor an artefact box based on firing angle, pixel number, and distance ofcorresponding to the pulse information of the non-targeted pixels. Thenon-targeted scene processor 62 transmits the artefact box parameters tothe crosstalk processing circuit 70. Thus, the non-targeted sceneprocessing circuit 62 performs the first step of the three step approachdescribed above (i.e., the detection and flagging step).

The crosstalk processing circuit 70 receives the detected TOF hits fromthe targeted scene processing circuit 61 and the artefact box parametersfrom the non-targeted scene processing circuit 62, and uses the receivedinformation to perform the second and third steps of the three stepapproach described above (i.e., the artefact probability scoring stepand the probability thresholding step).

Based on the results of the probability thresholding step, the crosstalkprocessing circuit 70 transmits ToF data and possibly crosstalkinformation to a point cloud processing circuit 80 that is configured togenerate point cloud data based thereon and output a point cloud.

Although some aspects have been described in the context of anapparatus, it is clear that these aspects also represent a descriptionof the corresponding method, where a block or device corresponds to amethod step or a feature of a method step. Analogously, aspectsdescribed in the context of a method step also represent a descriptionof a corresponding block or item or feature of a correspondingapparatus. Some or all of the method steps may be executed by (or using)a hardware apparatus, like for example, a microprocessor, a programmablecomputer, or an electronic circuit. In some embodiments, some one ormore of the method steps may be executed by such an apparatus.

Depending on certain implementation requirements, embodiments providedherein can be implemented in hardware or in software. The implementationcan be performed using a digital storage medium, for example a floppydisk, a DVD, a Blue-Ray, a CD, a ROM, a PROM, an EPROM, an EEPROM or aFLASH memory, having electronically readable control signals storedthereon, which cooperate (or are capable of cooperating) with aprogrammable computer system such that the respective method isperformed. Therefore, the digital storage medium may be computerreadable.

Instructions may be executed by one or more processors, such as one ormore central processing units (CPU), digital signal processors (DSPs),general purpose microprocessors, application specific integratedcircuits (ASICs), field programmable logic arrays (FPGAs), or otherequivalent integrated or discrete logic circuitry. Accordingly, the term“processor,” as used herein refers to any of the foregoing structures orany other structure suitable for implementation of the techniquesdescribed herein. In addition, in some aspects, the functionalitydescribed herein may be provided within dedicated hardware and/orsoftware modules. Also, the techniques could be fully implemented in oneor more circuits or logic elements.

The above described exemplary embodiments are merely illustrative. It isunderstood that modifications and variations of the arrangements and thedetails described herein will be apparent to others skilled in the art.It is the intent, therefore, to be limited only by the scope of theimpending patent claims and not by the specific details presented by wayof description and explanation of the embodiments herein.

1. A Light Detection and Ranging (LIDAR) system, comprising: a LIDARtransmitter configured to scan a field of view with a plurality of lightbeams, each of the plurality of light beams having an oblong shape thatextends perpendicular to a scanning direction, the LIDAR transmittercomprising: a light source array comprising a plurality of light sourcesconfigured to generate a scanning light bar such that each of theplurality of light sources is configured to project into a differentregion of a plurality of regions of the field of view; and a controllerconfigured to trigger a measurement of the field of view during which atleast one targeted region of the field of view is illuminated by thelight source array and at least one non-targeted region of the field ofview is not illuminated by the light source array; and a LIDAR receivercomprising: a photodetector array configured to receive at least onereflected light beam and generate electrical signals based on the atleast one reflected light beam, wherein the photodetector arraycomprises a targeted pixel group that corresponds to the at least onetargeted region of the field of view and a non-targeted pixel group thatcorrespond to the at least one non-targeted region of the field of view;and an optical crosstalk detection circuit configured to receive atleast one first electrical signal from the targeted pixel group and atleast one second electrical signal from the non-targeted pixel group,detect optical crosstalk that appears at at least one portion of thenon-targeted pixel group based on the at least one first electricalsignal and the at least one second electrical signal, and define a glareartefact box corresponding to pixels of the photodetector array anddefined by the detected optical crosstalk.
 2. The LIDAR system of claim1, wherein the optical crosstalk detection circuit is configured todefine the glare artefact box based on at least one transmission angle,at least one pixel number, and at least one distance at which theoptical crosstalk is detected.
 3. The LIDAR system of claim 1, wherein:the optical crosstalk detection circuit is further configured to readout an entire array of the photodetector array for a predeterminedmeasurement period and detect optical crosstalk based on the electricalsignals generated by the entire array during the predeterminedmeasurement period.
 4. The LIDAR system of claim 3, wherein the at leastone second electrical signal includes a first time-of-flight (TOF)signal and a second TOF signal both generated by a first pixel of thephotodetector array during the predetermined measurement period, whereinthe first TOF signal has an earlier TOF than the second TOF signal andthe optical crosstalk detection circuit is configured to determine thatthe optical crosstalk corresponds to the first TOF signal of the firstpixel.
 5. The LIDAR system of claim 1, wherein: the optical crosstalkdetection circuit is configured to measure a time-of-flight (TOF)corresponding to each of the at least one first electrical signal andthe at least one second electrical signal, and detect the opticalcrosstalk at the at least one portion of the non-targeted pixel groupbased on the at least one first electrical signal and the at least onesecond electrical signal having a same TOF.
 6. The LIDAR system of claim1, wherein: the optical crosstalk detection circuit is configured tomeasure an amplitude corresponding to each of the at least one firstelectrical signal and the at least one second electrical signal, anddetect the optical crosstalk at the at least one portion of thenon-targeted pixel group based the amplitude of the at least one secondelectrical signal decreasing as a distance of the at least one portionof the non-targeted pixel group increases from the targeted pixel group.7. The LIDAR system of claim 1, wherein the optical crosstalk detectioncircuit is configured to, in response to detecting the opticalcrosstalk, record a pixel number for each pixel of the non-targetedpixel group at which the optical crosstalk is detected.
 8. The LIDARsystem of claim 1, wherein the optical crosstalk detection circuit isconfigured to, in response to detecting the optical crosstalk, record atime-of-flight corresponding to the at least one reflected light beamfor each pixel of the non-targeted pixel group at which the opticalcrosstalk is detected.
 9. The LIDAR system of claim 1, wherein theoptical crosstalk detection circuit is configured to, in response todetecting the optical crosstalk, record a transmission anglecorresponding to the at least one reflected light beam for each pixel ofthe non-targeted pixel group at which the optical crosstalk is detected.10. The LIDAR system of claim 1, wherein: the plurality of regionsinclude the at least one targeted region and the at least onenon-targeted region, and each of the plurality of regions extends from afirst edge of the field of view to a second edge of the field of viewopposite to the first edge.
 11. The LIDAR system of claim 1, wherein theLIDAR transmitter further comprises: a one-dimensionalmicroelectromechanical systems (MEMS) oscillating structure configuredto oscillate about a single scanning axis and reflectively transmit theplurality of laser beams such that a scanning line moves across thefield of view in the scanning direction as the one-dimensional MEMSoscillating structure oscillates about the single scanning axis.
 12. TheLIDAR system of claim 1, wherein: the controller is configured totrigger a plurality of measurements of the field of view, wherein, overthe plurality of measurements, the controller is configured tosequentially activate different first portions of the plurality of lightsources corresponding to different targeted regions of the field of viewwhile sequentially deactivating different second portions of theplurality of light sources corresponding to different non-targetedregions of the field of view, and the optical crosstalk detectioncircuit is configured to detect at least one common glare artefactproperty between at least one of the different targeted regions and atleast one of the different non-targeted regions, and detect opticalcrosstalk that appears at the at least one of the different non-targetedregions based on the at least one detected common glare artefactproperty.
 13. The LIDAR system of claim 1, wherein: the opticalcrosstalk detection circuit is configured to detect at least one commonglare artefact property between the at least one first electrical signaland the at least one second electrical signal, and detect the opticalcrosstalk that appears at the at least one portion of the non-targetedpixel group based on the at least one detected common glare artefactproperty.
 14. The LIDAR system of claim 1, wherein: the opticalcrosstalk detection circuit is configured to assign a likelihood scoreto each of the electrical signals, including the at least one firstelectrical signal and the at least one second electrical signal, compareeach likelihood score to a likelihood threshold, and identify the atleast one portion of the non-targeted pixel group corresponding the atleast one second electrical signal having a likelihood score less thanthe likelihood threshold.
 15. The LIDAR system of claim 14, wherein: theoptical crosstalk detection circuit is configured to detect an opticalcrosstalk that appears at at least one portion of the targeted pixelgroup based on the at least one first electrical signal and the at leastone second electrical signal, wherein the optical crosstalk detectioncircuit is configured identify the at least one portion of the targetedpixel group corresponding the at least one first electrical signalhaving a likelihood score less than the likelihood threshold.
 16. TheLIDAR system of claim 14, further comprising: a point cloud generatorconfigured to generate a point cloud based on the electrical signals,wherein the optical crosstalk detection circuit is configured to report,to the point cloud generator, sensor data corresponding to theelectrical signals having a likelihood score greater than the likelihoodthreshold, and wherein the optical crosstalk detection circuit isconfigured to discard sensor data corresponding to the electricalsignals having a likelihood score less than the likelihood threshold orreport, to the point cloud generator, the sensor data corresponding tothe electrical signals having the likelihood score less than thelikelihood threshold along with a respective likelihood score.
 17. Amethod of detecting optical crosstalk in a Light Detection and Ranging(LIDAR) system, the method comprising: oscillating a one-dimensionalmicroelectromechanical systems (MEMS) oscillating structure about asingle axis such that light beams generated by a plurality of lightsources of a linear light source array are projected at differenttransmission directions into a field of view; selectively activating anddeactivating the plurality of light sources, wherein each of theplurality of light sources is configured to project a light beam as adifferent segment of a scanning line into a corresponding region of aplurality of regions of the field of view; triggering a measurement ofthe field of view during which at least one targeted region of the fieldof view is illuminated by the light source array and at least onenon-targeted region of the field of view is not illuminated by the lightsource array; generating electrical signals based on at least onereflected light beam being received by a photodetector array, whereinthe photodetector array comprises a targeted pixel group thatcorresponds to the at least one targeted region of the field of view anda non-targeted pixel group that correspond to the at least onenon-targeted region of the field of view; processing at least one firstelectrical signal from the targeted pixel group; processing at least onesecond electrical signal from the non-targeted pixel group; detectingoptical crosstalk that appears at at least one portion of thenon-targeted pixel group based on the at least one first electricalsignal and the at least one second electrical signal; and defining aglare artefact box corresponding to pixels of the photodetector arrayand defined by the detected optical crosstalk.
 18. The method of claim17, wherein defining the glare artefact box includes defining the glareartefact box based on at least one transmission angle, at least onepixel number, and at least one distance at which the optical crosstalkis detected.
 19. The method of claim 17, further comprising: detectingat least one common glare artefact property between the at least onefirst electrical signal and the at least one second electrical signal;and detecting the optical crosstalk that appears at the at least oneportion of the non-targeted pixel group based on the at least onedetected common glare artefact property.
 20. The method of claim 17,further comprising: triggering a plurality of measurements of the fieldof view; during the plurality of measurements, sequentially activatingdifferent first portions of the plurality of light sources correspondingto different targeted regions of the field of view while sequentiallydeactivating different second portions of the plurality of light sourcescorresponding to different non-targeted regions of the field of view;detecting at least one common glare artefact property between at leastone of the different targeted regions and at least one of the differentnon-targeted regions; and detecting optical crosstalk that appears atthe at least one of the different non-targeted regions based on the atleast one detected common glare artefact property.
 21. The method ofclaim 17, further comprising: assigning a likelihood score to each ofthe electrical signals, including the at least one first electricalsignal and the at least one second electrical signal; comparing eachlikelihood score to a likelihood threshold; and identifying the at leastone portion of the non-targeted pixel group corresponding to the atleast one second electrical signal having a likelihood score less thanthe likelihood threshold.
 22. The method of claim 17, furthercomprising: for the triggered measurement, reading out an entire portionof the of the photodetector array for a predetermined measurementperiod, wherein the at least one second electrical signal includes afirst time-of-flight (TOF) signal and a second TOF signal both generatedby a first pixel of the photodetector array during the predeterminedmeasurement period, wherein the first TOF signal has an earlier TOF thanthe second TOF signal, and determining that the optical crosstalkcorresponds to one of the first TOF signal or the second TOF signal ofthe first pixel.
 23. The method of claim 17, further comprising:measuring a time-of-flight (TOF) corresponding to each of the at leastone first electrical signal and the at least one second electricalsignal; and detecting the optical crosstalk at the at least one portionof the non-targeted pixel group based on the at least one firstelectrical signal and the at least one second electrical signal having asame TOF.